An Etymological Dictionary of the German Language/Annotated/Gienmuschel

Gienmuschel, feminine, ‘a species of tellina,’ allied to Middle High German ginen (gienen), ‘to gape, open the mouth wide,’ Old High German ginên; the latter is derived from an Old Teutonic root gī̆ (Aryan ghī̆), ‘to bark, gape, open the mouth wide.’ See gähnen.